Lab Notebook: My First OSPF Adjacency That Would Not Form
A troubleshooting walkthrough: timers, area IDs, and the passive-interface line hiding in plain sight.
Symptoms first, theories second
The adjacency stuck in EXSTART. Before changing anything, I captured the symptom precisely: which state, on which interface, with what neighbor output.
Writing the symptom down kept me from fixating on the first theory that felt right.
The checklist that found it
Area ID match, hello/dead timers match, MTU match, network statements, passive interfaces, authentication. Walking the list in order found a passive-interface statement I had added and forgotten.
Boring checklists beat clever guesses. Every time, so far.
Related reading
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The paper-first checklist I use for small VLAN designs: inventory, addressing, trunk map, and test cases.
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Lessons from auditing my own accounts: recovery codes, authenticator backups, and the accounts I almost missed.